U.S. patent number 6,577,283 [Application Number 09/835,789] was granted by the patent office on 2003-06-10 for dual frequency coaxial feed with suppressed sidelobes and equal beamwidths.
This patent grant is currently assigned to Northrop Grumman Corporation. Invention is credited to Andrew L. Roberts, Teh-Kan Tung, Te-Kao Wu.
United States Patent |
6,577,283 |
Wu , et al. |
June 10, 2003 |
Dual frequency coaxial feed with suppressed sidelobes and equal
beamwidths
Abstract
An antenna feed in a satellite system that provides
substantially equal E-plane and H-plane patterns. The feed includes
outer and inner conductive walls that are coaxial, and define an
outer waveguide therebetween and an inner waveguide within the
inner conductive wall. The feed includes a first cylindrical
waveguide section, a tapered waveguide section, and a second
cylindrical waveguide section at the aperture of the feed. Downlink
signals are in signal communication with the first cylindrical
waveguide section so that the downlink signals are launched into
the outer waveguide and out of the feed. Uplink signals received by
the inner waveguide are directed to suitable uplink reception
devices. One or both of the outer or inner conductive walls include
an array of radially disposed iris pins at the aperture that
interact with the uplink and/or downlink signals to provide beam
symmetry or equal E-plane and H-plane patterns.
Inventors: |
Wu; Te-Kao (Rancho Palos
Verdes, CA), Tung; Teh-Kan (Irvine, CA), Roberts; Andrew
L. (Frazier Park, CA) |
Assignee: |
Northrop Grumman Corporation
(Redondo Beach, CA)
|
Family
ID: |
25270464 |
Appl.
No.: |
09/835,789 |
Filed: |
April 16, 2001 |
Current U.S.
Class: |
343/786; 343/789;
343/791 |
Current CPC
Class: |
H01Q
13/025 (20130101); H01Q 5/40 (20150115) |
Current International
Class: |
H01Q
13/00 (20060101); H01Q 5/00 (20060101); H01Q
13/02 (20060101); H01D 005/12 (); H01Q 013/02 ();
H01Q 001/42 () |
Field of
Search: |
;343/791,786,783,772,183,789,776,790,795,797,816 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
CE. Profera, "Improvement of TE11 Mode Coaxial Waveguide and Horn
Radiation Patterns by Incorporation of a Radial Aperture
Reactance," IEEE Trans., vol. AP-24, Mar. 1976, pp. 203-206. .
J.C. Lee, "A Compact Q/K Band Dual; Frequency Feed Horn," IEEE
Trans., vol. AP-32, Oct. 1984, pp. 1108-111..
|
Primary Examiner: Wong; Don
Assistant Examiner: Tran; Chuc
Attorney, Agent or Firm: Warn, Burgess & Hoffman,
P.C.
Claims
What is claimed is:
1. A coaxial feed for an antenna system, said feed transmitting an
output signal, said feed comprising: an outer conductive wall; an
inner conductive wall coaxial with the outer wall and defining an
outer waveguide therebetween and an inner waveguide within the
inner conductive wall; and a plurality of outer iris pins
symmetrically disposed around an opening of the outer waveguide,
said iris pins extending across the outer waveguide, said outer
iris pins being flat and thin members, said iris pins providing
suppressed sidelobes and substantially equal E-plane and H-plane
radiation patterns of the signal.
2. The feed according to claim 1 wherein the outer and inner
conductive walls are cylindrical.
3. A coaxial feed for an antenna system, said feed transmitting an
output signal, said feed comprising: an outer conductive wall; an
inner conductive wall coaxial with the outer wall and defining an
outer waveguide therebetween and an inner waveguide within the
inner conductive wall; and a plurality of outer iris pins radially
disposed symmetrically around an opening of the outer waveguide so
as to define a predetermined space between adjacent pins, said iris
pins extending across the outer waveguide, wherein each of the
outer iris pins has a trapezoidal shape when viewed in a direction
facing the opening so that the predetermined spaces between each
pair of adjacent outer iris pins is rectangular, said iris pins
providing substantially equal E-plane and H-plane radiation
patterns of the signal.
4. A coaxial feed for an antenna system, said feed transmitting an
output signal, said feed comprising: an outer conductive wall; an
inner conductive wall coaxial with the outer wall and defining an
outer waveguide therebetween and an inner waveguide within the
inner conductive wall; and a plurality of outer iris pins
symmetrically disposed around an opening of the outer waveguide,
said iris pins extending across the outer waveguide and having a
length less than the distance between the outer conductive wall and
the inner conductive wall, said outer iris pins being flat and thin
members, said iris pins providing suppressed sidelobes and
substantially equal E-plane and H-plane radiation patterns of the
signal.
5. A coaxial feed for an antenna system, said feed transmitting an
output signal, said feed comprising: an outer conductive wall; an
inner conductive wall coaxial with the outer wall and defining an
outer waveguide therebetween and an inner waveguide within the
inner conductive wall, said inner and outer conductive walls each
having a first cylindrical coaxial section, a tapered section
coupled to the first cylindrical coaxial section, and a second
cylindrical coaxial section coupled to the tapered section, said
outer waveguide having an opening at an output of the second
cylindrical section opposite to the first cylindrical section; and
a plurality of outer iris pins symmetrically disposed around said
outer waveguide opening, said iris pins extending across the outer
waveguide, said outer iris pins being flat and thin members, said
iris pins providing suppressed sidelobes and substantially equal
E-plane and H-plane radiation patterns of the signal.
6. A coaxial feed for an antenna system, said feed transmitting an
output signal, said feed comprising: an outer conductive wall; an
inner conductive wall coaxial with the outer wall and defining an
outer waveguide therebetween and an inner waveguide within the
inner conductive wall, wherein the inner waveguide is at the center
of the feed; a plurality of outer iris pins symmetrically disposed
around an opening of the outer waveguide, said iris pins extending
across the outer waveguide, said outer iris pins being flat and
thin members, said iris pins providing suppressed sidelobes and
substantially equal E-plane and H-plane radiation patterns of the
output signal; and a plurality of inner iris pins symmetrically
disposed around an opening of the inner waveguide, said inner iris
pins being flat and thin members, said inner iris pins providing
suppressed sidelobes and equal E-plane and H-plane radiation
patterns of an input signal.
7. A coaxial feed for an antenna system on a satellite, said feed
transmitting a satellite downlink signal and receiving a satellite
uplink signal, said feed comprising: an outer conductive wall; an
inner conductive wall coaxial with the outer wall and defining an
outer waveguide between the inner conductive wall and the outer
conductive wall and an inner waveguide within the inner conductive
wall, said inner and outer conductive walls having a first
cylindrical coaxial section, a tapered section coupled to the first
cylindrical coaxial section and a second cylindrical coaxial
section coupled to the tapered section, said second coaxial section
having an aperture opposite to the first cylindrical section; and a
plurality of outer iris pins radially disposed around the aperture
of the outer waveguide and extending across the outer waveguide,
wherein each of the outer iris pins has a trapezoidal shape when
viewed in a direction facing the aperture so as to define
rectangular spaces between each pair of adjacent outer iris pins,
said iris pins providing equal E-plane and H-plane patterns of the
satellite downlink signal.
8. The feed according to claim 7 wherein the iris pins have a
length less than the distance between the outer conductive wall and
the inner conductive wall.
9. A coaxial feed for an antenna system on a satellite, said feed
transmitting a satellite downlink signal and receiving a satellite
uplink signal, said feed comprising: an outer conductive wall; an
inner conductive wall coaxial with the outer wall and defining an
outer waveguide between the inner conductive wall and the outer
conductive wall and an inner waveguide within the inner conductive
wall, wherein the inner waveguide is at the center of the feed,
said inner and outer conductive walls having a first cylindrical
coaxial section, a tapered section coupled to the first cylindrical
coaxial section and a second cylindrical coaxial section coupled to
the tapered section, said section coaxial section having an
aperture opposite to the first cylindrical section; a plurality of
outer iris pins radially disposed around the aperture of the outer
waveguide and extending across the outer waveguide, said outer iris
pins being flat and thin members, said outer iris pins providing
suppressed sidelobes and equal E-plane and H-plane patterns of the
satellite downlink signal; and a plurality of inner iris pins
symmetrically disposed around the aperture of the inner waveguide,
said inner iris pins being flat and thin members, said inner iris
pins providing suppressed sidelobes and equal E-plane and H-plane
patterns of an input signal.
10. The feed according to claim 9 wherein the plurality of inner
iris pins have a length less than half the diameter of the inner
waveguide.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a dual frequency coaxial feed
for an antenna feed horn and, more particularly, to a dual
frequency coaxial feed for an antenna feed horn on a satellite that
employs an array of conductive iris pins at the aperture of the
feed to suppress side-lobes and provide equal E-plane and H-plane
patterns.
2. Discussion of the Related Art
Various communications systems, such as certain cellular telephone
systems, cable television systems, Internet systems, military
communications systems, etc., make use of satellites orbiting the
Earth to transfer signals. A satellite uplink communications signal
is transmitted to the satellite from one or more ground stations,
and is then retransmitted by the satellite to another satellite or
to the Earth as a downlink communications signal to cover a
desirable reception area depending on the particular use. The
uplink and downlink signals are typically transmitted at different
frequency bandwidths. For example, the uplink communications signal
may be transmitted at 30 GHz and the downlink communications signal
may be transmitted at 20 GHz.
The satellite is equipped with an antenna system including a
configuration of antenna feeds that receive the uplink signals and
transmit the downlink signals to the Earth. Typically, the antenna
system includes one or more arrays of feed horns, where each feed
horn array includes an antenna reflector for collecting and
directing the signals. In order to reduce weight and conserve the
satellite real estate, some satellite communications systems use
the same antenna system and array of feed horns to receive the
uplink signals and transmit the downlink signals. Combining
satellite uplink signal reception and downlink signal transmission
functions for a particular coverage area using a reflector antenna
system requires specialized feed systems capable of supporting dual
frequencies and providing dual polarization, and thus requires
specialized feed system components. These specialized feed system
components include signal orthomode couplers, such as coaxial
turnstile junctions, known to those skilled in the art, in
combination with each feed horn to provide signal combining and
isolation to separate the uplink and downlink signals. Also, the
downlink signal, transmitted at higher power (60-100 W) at the
downlink bandwidths (18.3 GHz-20.2 GHz), requires low losses and
special design for high power and temperature capability feeds.
The uplink and downlink signals are circularly polarized so that
the orientation of the reception antenna can be arbitrary relative
to the incoming signal. To provide signal discrimination or
frequency reuse, one of the signals may be left hand circularly
polarized (LHCP) and the other signal may be right hand circularly
polarized (RHCP), where the signals rotate in opposite directions.
Polarizers are employed in the antenna system to convert the
circularly polarized signals to linearly polarized signals suitable
for propagation through a waveguide with low signal losses, and
vice versa.
One example of an antenna feed for an antenna feed horn used in the
antenna systems discussed above is referred in the industry as the
Milstar dual band feed. The Milstar dual band feed employs a
coaxial design where concentric inner and outer conductive walls
define an outer waveguide cavity and an inner waveguide cavity. The
downlink signal is transmitted through the outer waveguide cavity
and out of a tapered corrugated feed horn, and the uplink signal is
received by the same horn and is directed through the inner
waveguide cavity. A tapered dielectric is positioned at the
aperture of the inner waveguide cavity to provide impedance
matching between the feed horn and the inner waveguide cavity, and
also launches the uplink signal into the inner waveguide cavity so
that it is above the waveguide cut-off frequency. The inner surface
of the feed horn is corrugated to provide a symmetrical pattern
signal for both the uplink and downlink signals for equal E-plane
and H-plane matching. The feed horn is tapered to provide an
aperture suitable for illuminating the reflector associated with
the antenna system.
The Milstar dual band feed suffers from a number of drawbacks that
can be improved upon. For example, the dielectric and the inner
waveguide cavity must be carefully aligned and tuned to provide a
suitable axial ratio for the uplink signal. Additionally, because
the downlink signal is at high power, it tends to cause breakdown
in the dielectric, reducing its capability. Thus, the intensity of
the downlink signal must be limited in certain applications.
Further, the corrugated feed horn is heavy, and adds significant
size to the overall size of the feed.
What is needed is a feed for a satellite antenna system that is
lightweight, easy to manufacture, and provides equal E-plane and
H-plane signals with suppressed side-lobes. It is therefore an
object of the present invention to provide such a feed horn.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, an
antenna feed for a feed array in a satellite antenna system is
disclosed that is lightweight, easy to manufacture, and provides
equal E-plane and H-plane signals. The feed includes an outer
cylindrical conductor and an inner cylindrical conductor that are
coaxial, and define an outer waveguide cavity therebetween and an
inner waveguide cavity within the inner conductor. The feed also
includes a first cylindrical waveguide section, a tapered waveguide
section, and a second cylindrical waveguide section at the aperture
of the feed. Downlink waveguides are in signal communication with
the first cylindrical waveguide section so that downlink signals
are launched into the outer waveguide cavity and out of the feed.
Uplink signals received by the inner waveguide cavity are directed
to suitable uplink reception devices.
According to the invention, one or both of the outer or inner
conductors at the aperture of the second cylindrical waveguide
includes an array of radially disposed iris pins that interact with
the uplink and/or downlink signals to provide beam symmetry, equal
E-plane and H-plane signals, and suppressed side-lobes.
Additional objects, features and advantages of the present
invention will become apparent from the following description and
appended claims, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a length-wise cross-sectional view of a feed for a
satellite antenna system, according to an embodiment of the present
invention;
FIG. 2 is a front view of the feed shown in FIG. 1;
FIG. 3 is a graph with amplitude in dB on the vertical axis and
degrees on the horizontal axis showing the radiation pattern for
the H-plane and E-plane signals of a conventional dual band coaxial
feed configuration; and
FIG. 4 is a graph with amplitude in dB on the vertical axis and
degrees on the horizontal axis showing the radiation pattern for
the H-plane and E-plane signals for the feed of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The following discussion of the preferred embodiments directed to a
feed for an antenna on a satellite is merely exemplary in nature,
and is in no way intended to limit the invention or its application
to uses.
FIG. 1 is a length-wise, cross-sectional view of a feed 10 for a
satellite antenna system that receives a satellite uplink signal at
a particular frequency band, for example, 28-30 GHz or 44 GHz, and
transmits a downlink signal at another frequency band, for example,
18.3-20.3 GHz. As will be appreciated by those skilled in the art,
the feed 10 would be part of an array of feeds arranged in a
desirable manner depending on the particular application. The
antenna system may employ reflectors and the like for collecting
and directing the uplink and downlink signals depending on the
particular application. By employing feeds of the type discussed
herein, separate antenna systems are not needed for the satellite
uplink and downlink signals, and therefore valuable space on the
satellite can be conserved and the weight of the satellite can be
reduced.
The feed 10 includes a feed horn 12 having an outer conductive wall
14 and an inner conductive wall 16 made of a suitable conductive
metal. The outer wall 14 and the inner wall 16 are coaxial and
define an outer waveguide 18 and an inner waveguide 20. The feed
horn 12 includes a first cylindrical section 24, a tapered section
26 that expands the diameter of the feed horn 12 from the first
cylindrical section 24, and a second cylindrical section 28 at the
output of the feed horn 12. A mouth 30 of the section 28 defines an
aperture of the feed 10.
Uplink signals are received by the inner waveguide 20 and propagate
into the second cylindrical section 28, the tapered section 26, and
the first cylindrical section 24. Suitable reception circuitry and
devices (not shown) are provided downstream of the first
cylindrical section 24 that convert the circularly polarized uplink
signal to a linearly polarized signal suitable for the reception
devices within the reception circuitry. Low noise amplifiers,
receivers, and other reception devices would be provided to receive
the uplink signal, as would be appreciated by those skilled in the
art.
A downlink signal to be transmitted by the feed 10 enters the outer
waveguide 18 from a 0.degree. coaxial (SMA) input 36 and a
180.degree. coaxial SMA input 38. The coaxial SMA inputs 36 and 38
are connected to a power divider (not shown) that splits the
downlink signal into a suitable signal for transmission. A shorting
disk 40 is provided over the outer waveguide 18 opposite the mouth
30. This disk and the center pins of coaxial inputs 36 and 38 form
an efficient downlink signal launcher for the outer circular
waveguide.
In one embodiment for a particular application, the thickness of
the outer conductive wall 14 is 0.05 inches. Further, the internal
diameter of the first cylindrical section 24 defined by the outer
conductive wall 14 is 0.4514 inches and the diameter of the inner
waveguide 20 in the cylindrical section 24 is 0.2257 inches.
Additionally, the internal dimension of the outer waveguide 18 of
the second cylindrical section 28 is 1.048 inches and the diameter
of the inner waveguide 20 in the second cylindrical section is
0.524 inches. Further, the first cylindrical section 24 is 2 inches
long, the tapered section 26 is 2.1225 inches long, and the second
cylindrical section 28 is 2 inches long. These dimensions are by
way of a non-limiting example, in that other dimensions for other
feeds would be applicable for different applications.
According to the invention, a plurality of outer waveguide iris
pins 44 are provided at the mouth 30 of the second cylindrical
section 28 so that they extend across the waveguide 18 and
transverse to the propagation direction of the downlink signal. The
iris pins 44 are spaced apart a predetermined distance and are
radially disposed around the entire circumference of the mouth 30.
Also, a plurality of iris pins 46 are provided at the mouth 30 of
the second cylindrical section 28 so that they extend across the
inner waveguide 20 and transverse to the propagation directions of
the uplink signal. The iris pins 46 are also radially disposed
around the complete circumference of the inner conductor 16. The
iris pins 44 and 46 interact with the downlink signals and the
uplink signals, respectively, to provide equal E-plane and H-plane
signals and a circular polarized (CP) signal with less than 0.5 dB
axial ratio. In other words, the iris pins 44 and 46 provide the
function of the corrugations in the known Milstar dual band feed.
As is apparent, the iris pins 44 do not extend completely across
the waveguide 18, and the iris pins 46 do not extend completely
halfway across the diameter of the inner waveguide 20. In this
embodiment, as shown in FIG. 1, the iris pins 44 and 46 are flat
and thin members to provide the benefits as discussed herein.
FIG. 2 is a front view of a feed 10' that is intended to represent
a front view of the feed 10 with the irises 46 removed. In this
regard, like components are labeled with the same reference numeral
and a prime. As is apparent, the iris pins 44' are
trapezoidal-shaped defining a rectangular space 50 between adjacent
pins 44. The iris pins 44' extend almost completely across the
aperture of the outer waveguide 18, as shown. By providing the iris
pins 44' in this configuration, the E-plane portions of the
downlink signal interacts with the iris pins 44' so that the field
is suppressed and is made equal to the H-plane. Thus, the E-plane
and H-plane signals are equalized providing a more circularly
polarized signal. Therefore, a more symmetric circularly polarized
downlink signal can be provided having a small axial ratio, low
side-lobes and low-cross polarization.
In this example, there are twenty-four pins 44", spaced every
15.degree. around the aperture of the outer waveguide 18. Further,
the spaces 50 are about 0.032 inches wide and about 1.048 inches in
diameter. However, these dimensions are by way of a non-limiting
example in that other downlink frequencies and designs may require
more or less iris pins, more or less space between the iris pins,
etc.
FIG. 3 is a graph with amplitude in dB on the vertical axis and
degrees on the horizontal axis showing the H-plane and E-plane
signals for a conventional dual band coaxial feed configuration. As
is apparent, the H-plane and E-plane patterns are somewhat unequal,
increasing the CP signals axial ratio. FIG. 4 is a graph with
amplitude in dB on the vertical axis and degrees on the horizontal
axis showing that the H-plane and E-plane patterns for the feeds 10
and 10' are substantially equal over the main lobe of the pattern,
and have low side-lobes.
The foregoing discussion discloses and describes merely exemplary
embodiments of the present invention. One skilled in the art will
readily recognize from such discussion, and from the accompanying
drawings and claims, that various changes, modifications and
variations can be made therein without departing from the spirit
and scope of the invention as defined in the following claims.
* * * * *